Beef thyroid membrane adenylate cyclase has been solubilized by nonionic detergents and characterized. Differences from the membrane-bound enzyme are in pH optimum, response to stimulators and inhibition by a variety of compounds effective on membranes. In addition, the relation between cationic and detergent properties of the basic protein melittin has been investigated. The detergent-like properties are the main determinants in the inhibitory effect on adenylate clcylase. BIBLIOGRAPHIC REFERENCES: Wolff, J.: Hormone and Antihormone Action at the Target Cell. In Clark, J.H., Klee, W., Levitzki, A. and Wolff, J. (Eds.): Life Sciences Research Report 1. Berlin, Dahlem Konferenzen, 1976, vol. 3, 226 pp.